In the medical field, for example, medical image software or visualization systems using computer graphics or image processing techniques are extensively used. In computer-aided diagnoses or preoperative planning, an environment is necessary in which a region of interest on a medical image can be flexibly and interactively referred to (see Non-Patent Documents 1 and 2, for example).
Herein, a collection of two-dimensional images acquired by CT or MRI is volume data constituted by a huge number of voxels. In order to provide intuitive understanding of a complex three-dimensional structure inside the human body, it is necessary to render the structure together with its interior.
In conventional information processing apparatuses for this request, typically, a three-dimensionally reconstructed image using display of sliced tomographic images or volume rendering is used in preoperative planning or intraoperative navigation (see Non-Patent Documents 3 and 4, for example). Furthermore, clipping expression at an arbitrary plane on a reconstructed image is extensively used for observing the interior of an organ (see Non-Patent Document 5, for example).
Furthermore, as a conventional information processing apparatus, there is an interactive system such as a VR surgical simulator. This interactive system uses polygons in order to define a three-dimensional geometric shape (see Non-Patent Document 6, for example).
Herein, as an input/output device relating to this information processing apparatus, there is PHANToM. PHANToM is an input/output device for receiving input of positional data, giving feedback to a computer, and generating a force vector and driving a motor (see Non-Patent Document 7, for example).
Furthermore, as a technique relating to the present invention, there are an algorithm for calculating deformation (Non-Patent Document 8, for example) and an algorithm for rendering (Non-Patent Document 9, for example).
Also, recently, radiotherapy is attracting attention as a method for effectively treating cancer. However, there is the problem that if an affected area moves due to breathing as in the case of lung tumors, an efficient treatment is difficult. Currently, countermeasures are taken such as setting a wide irradiation area, or implementing a marker in the vicinity of a tumor and irradiating this position in synchronization with breathing. In a radiotherapy apparatus that is currently under development, an accelerator tube for generating radiation includes a gimbal function, and thus a head can be freely swung. There is a demand for a treatment in which a tumor is irradiated with radiation while being tracked using these characteristics.    [Non-Patent Document 1] J. Toriwaki and one other, “Visualization of the Human Body toward the Navigation Diagnosis with the Virtualized Human Body”, Journal of Visualization, 1998, Vol. 1, No. 1, pp. 111-124.    [Non-Patent Document 2] B. Pflesser and three others, “Planning and Rehearsal of Surgical Interventions in the Volume Model”, Proc. Medicine Meets Virtual Reality Conference, 2000, pp. 259-264.    [Non-Patent Document 3] A. Kaufman and two others, “Volume Graphics”, IEEE Computer, 1993, Vol. 26, No. 7, pp. 51-64.    [Non-Patent Document 4] W. Chen and two others, “Real-time Ray Casting Rendering of Volume Clipping in Medical Visualization”, Journal of Computer Science and Technique, 2003, Vol. 18, Issue 6, pp. 804-814.    [Non-Patent Document 5] B. Cabral and two others, “Accelerated Volume Rendering and Tomographic Reconstruction Using Texture Mapping Hardware”, Proc. Symposium on Volume Visualization '94, 1994, pp. 91-98.    [Non-Patent Document 6] U. Kuhnapfel and two others, “Endoscopic Surgery Training Using Virtual Reality and Deformable Tissue Simulation”, Computers & Graphics (Elsevier Science), 2000, Vol. 24, No. 5, pp. 671-682.    [Non-Patent Document 7] Website, the Internet <URL: http://www.nissho-ele.co.jp/3d/3Dmodeling/phamtom03.htm>    [Non-Patent Document 8] Yasuhiro Yamamoto et al., “Palpation Simulator of Beating Aorta for Cardiovascular Surgery Training”, Journal of the Institute of Electrical Engineers of Japan, 2003, Vol. 123-E, No. 3, pp. 85-92.    [Non-Patent Document 9] Megumi Nakao and two others, “Volumetric Mask and its Real-time Processing for Volume Interaction”, Journal of the Virtual Reality Society of Japan, 2005, Vol. 10, No. 4, pp. 591-598.